Effects of yogurt ingestion on mucosal and systemic cytokine gene expression in the mouse.

To assess the potential for ingestion of yogurt to modulate immunity, its effects on basal gene expression of cytokines in systemic and mucosal sites were determined in mice. Yogurts were manufactured from pasteurized nonfat dry milk using five commercial starter cultures with or without Bifidobacterium sp. and Lactobacillus acidophilus. Treatment mice were fed the AIN-93G diet mixed 1:1 with unheated yogurt or heat-treated yogurt (wt/wt) for 2 and 4 weeks, and control mice were fed the AIN-93G diet mixed 1:1 (wt/wt) with nonfat dry milk. The viability of the various bacterial groups in unheated yogurts was maintained above 10(6) CFU/g throughout the feeding period. The yogurt-feeding regimens did not significantly affect weight gain. Relative mRNA levels in spleen, mesenteric lymph nodes, or Peyer's patches for the cytokines interferon-gamma, tumor necrosis factor-alpha, interleukin-2, -4, and -6, and the "housekeeping gene" beta2-microglobulin were determined by reverse transcriptase-polymerase chain reaction in conjunction with hybridization analysis. Prolonged feeding of some yogurts decreased expression of several cytokine mRNAs, the depression of tumor necrosis factor-alpha mRNA in the spleen being the most prominent effect. Heat-treated yogurts were more effective in altering cytokine mRNA expression than were unheated yogurts containing viable organisms. Generally, yogurts either had no effect or decreased specific cytokine mRNA in the test organs, regardless of whether they contained Bifidobacterium sp. and L. acidophilus. These results suggest that, in contrast with previous studies in vitro, some yogurt formulations may reduce rather than stimulate basal cytokine expression and that these effects are most prominent in the systemic compartment.